It is known per se from the prior art how to link a control system, for example a stored program control (SPC) or a programmable logic controller (PLC), with a system server which can be accessed by a client computer. The client computer can load HTML pages from the server computer, for example in order to display process values on a user interface. The link between an output field of the HTML page and the process value is permanently programmed, for example by means of a JAVA script or by means of OCX (OLE Control Extension).
A system for remotely accessing a control system via a commercial communications network is known from U.S. Pat. No. 6,061,603. FIG. 1 shows a block diagram of this already known system.
The system comprises a personal computer 8 with a browser program 10. The browser 10 can be a commercially available Internet browser such as, for example, Netscape Communication Navigator or Microsoft Internet Explorer. The browser program 10 is used for accessing what is known as a website 4 via the Internet 14 in order to display the contents of the website 4 on the monitor 12 of the personal computer 8 for a user 2.
The website 4 includes a network interface 16 with a unique Internet address 18 as well as a server computer 20 and an application program 22. The server computer 20 serves to interpret HTTP protocols and uses TCP/IP by means of TCP/IP stack 24 in order to interact with the network interface 16 and the application program 22. This enables the data to be transferred between the application program 22 and the user 2 via the Internet 14.
The application program supplies data from a control system 6. This data can be used by the user 2 for monitoring the controller, since said data can be transferred by means of the TCP/IP stack 24 from the website 4 via the Internet 14 to the personal computer 8 of the user 2. By this means a human-machine interface is created on the personal computer 8.
The user 2 can set up a connection to the Internet 14 by way of what is termed an Internet Service Provider (ISP) and then enter the address of the website 4 into the browser program 10. Using the browser 10 the user 2 can then, for example, read a homepage of the website 4 and download information from said website 4. In response to an input by the user 2 the browser 10 sends commands to the website 4, which commands are used by the application program 22 in order to display information which is provided by the control system 6. A disadvantage with this already known system is in particular that the application program 22 has to be programmed specifically for a particular control system 6 and permits no flexibility of any kind.
The document XP 002163955, “c-Internet connector box miniwebserver”, Operating Instructions Rev 2.0 Internet Connector Box, Xx, Xx (Oct. 7, 1999), 1-121 discloses a device (ICB) with an embedded Internet server with which dynamic Internet pages can be generated from an HTML template. Up to three devices which support a special protocol can be connected to the ICB device. In order to communicate with such devices, the ICB device uses an information element which the devices sent to the device in their initialization phase.
XP010365709, Emerging Technologies And Factory Automation, 1999, Proceedings, Etfa '99, 1999 7th IEEE International Conference On [sic] Barcelona, Spain 18-21 Oct. 1999, Piscataway, Ni, Usa, ieee, Us (18, Oct. 1999), 823-830 discloses a method for accessing fieldbus devices using a client computer via the Internet. Here, a database or an XML document is used to provide a description of the fieldbus devices. The content of the HTML pages is then generated using the information from the database or the XML document.